How to allow downloading multiple files in Mozila?

On loop 3 Kantu exhibits the following error:

[error][ignored]

only one not-created download allowed at a time

Did you enable (allow) file downloads in Firefox? See https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file#w_changing-download-actions

A screencast of what is going on in your case would be nice.